1. Field of the Invention
The present invention relates to liquid crystal display module, more particularly, to an inverter cover shield for liquid crystal display module.
2. Description of the Related Art
In general, flat panel displays are increasingly being used for portable devices because they are thin, lightweight, consume low power. Among the various types of flat panel display devices, liquid crystal display (LCD) devices are widely used for laptop computers and desktop monitors because of their superior resolution, and color display quality.
An LCD device uses the optical anisotropy and polarization properties of liquid crystal molecules to produce an image. Liquid crystal molecules have a definite orientation that results from their peculiar characteristics. The specific orientation can be modified by applying an electric field across the liquid crystal molecules. Due to optical anisotropy, the transmissivity of the LCD device to an incident depends upon the orientation of the liquid crystal molecules.
The LCD device has an upper substrate and a lower substrate with electrodes that are spaced apart and face each other. A liquid crystal material is interposed between the upper and the lower substrates. When an electric field is applied to the liquid crystal material due to a voltage across the electrodes corresponding to the upper and lower substrates, respectively, an alignment direction of the liquid crystal molecules is changed in accordance with the applied voltage. By controlling the applied voltage, the LCD device provides various transmittances to rays of light, thereby displaying an image.
The LCD device, however, does not emit the light by itself. The LCD device requires a light source. Usually, a backlight device is positioned behind the LCD panel. Backlight devices are classified into direct backlight type (or direct type) units and edge light type (or edge type) units, depending on the position of a lamp with regard to the LCD panel. With the direct type backlight, incident rays irradiating from the lamp are directly incident on the LCD panel. With the edge type backlight unit, rays from the lamp are incident on the LCD panel via a light guide or a reflector.
Nowadays, the direct type backlight is more common than the edge type backlight. However, since the direct type backlight assembly includes a plurality of lamps behind the LCD panel, the LCD module gets thicker. Therefore, a major issue is to design thinner LCD modules.
FIG. 1 is a cross sectional view of a peripheral portion of a related art LCD module. As shown in FIG. 1, the LCD module includes an LCD panel 100 for displaying images and a backlight assembly that emits artificial light toward the LCD panel 100. A top case 290 surrounds the LCD panel 100 and the backlight assembly and fastens the LCD panel 100 to the backlight assembly.
The backlight assembly mainly consists of lamps 210, a reflector 220, a diffusion sheet 240, a mold frame 280, a lamp supporter 281 and a panel guide 285. The mold frame 280 accommodates and buttresses portions of the backlight assembly. The lamp supporter 281 is located in an inner portion of the mold frame 280 and supports both edges of each lamp 210. The lamps 210 are disposed in parallel with each other underneath the LCD panel 100. The reflector 220 is disposed underneath the lamps 210 and reflects light emitted by the lamps toward the LCD panel 100 to prevent the light loss. The diffusion sheet 240 is located over the lamps 210, and disperses and diffuses the emitted and reflected light. The panel guide 285 is disposed over the diffusion sheet 240 and accommodates the prism sheet 250 and the LCD panel 100.
The LCD module further includes a bottom cover 230 underneath the mold frame 280. The bottom cover 230 protects and shields the lamps 210. An inverter 260 is disposed underneath the bottom cover 230 to supply electric power to the lamps 210 through internal wires 265. A cover shield 270 surrounds the inverter 260 at the bottom of the bottom cover 230 and protects the inverter 260 from external impact. The cover shield 270 and the bottom cover 230 isolate the inverter 260 by embracing and covering the inverter on all sides. The cover shield 270 is made of a metallic material to absorb electromagnetic waves.
As shown in FIG. 1, the cover shield 270 consists of an inner side 271, a bottom side 272 and an outer side 273. The bottom side 272 corresponds to the bottom side of the inverter 260. The inner side 271 is disposed below the bottom cover 230. The outer side 273 corresponds to an outer portion of the bottom cover 230 and bends upward to cover the sidewalls of the bottom cover 230 and mold frame 280. Furthermore, the outer side 273 of the cover shield 270 is in contact with the internal wire 265s extending from the inverter 260 to the lamps 210.
The cover shield 270 may cause a parasitic capacitance in the internal wires 265 because the outer side 273 of the cover shield 270 contacts the internal wires 265. Current may be drawn of the internal wires 265 through the contact with the cover shield 270, thereby generating a current leakage in the internal wires 265. Accordingly, the lamps 210 may not receive enough current. The impedance caused by both the cover shield 270 and the internal wires 265 may be calculated by the following equation:Xc=1/(2πfC)where “f” represents a frequency of the alternating current that is flowing through the internal wires 265, and “C” represents the parasitic capacitance generated between the outer side 273 and the internal wires 265. In the above equation, the impedance(Xc) will decrease if the frequency (f) increases or if the parasitic capacitance (C) increases with the contact area between the outer side 273 and the internal wires 265. Therefore, the current leakage will increase when the impedance decreases.
When current leakage increases, the inrush current in lamps 210 will be reduced and the luminance of the light emitted by the lamps 210 will be reduced. To prevent these disadvantages, the related art frequently employs insulating papers or other related appliances between the cover shield 270 and the internal wires 265. However, such insulating papers or related appliances require additional fabrication, thus increasing production cost.